Can The Tenant Move Out Before The Lease Has Expired? In Addition, Can He Receive His Security Deposit Back And How Long Can I Hold The Deposit?

I have a rental home in Maryland. My home is for sale. I have a tenant, and their lease does not expire until July 1, 2008. They have a security deposit that I am holding. I have given him The First Right of Refusal. He has declined the offer, due to he is not able to afford the property. He is now in the process of purchasing a home that he can afford.